In a servo write process in a magnetic disk apparatus, self-servo write is proposed, which means that the magnetic disk apparatus itself records servo information, such as a burst signal, in a blank medium without using a dedicated servo write apparatus. Self-servo write enables cost reductions in the servo write process.
In the self servo write, a head having a read element and a write element located at different positions is used. In the case of using such a head, a pitch between burst signal recording positions varies because of a change in a read and write offset representing a distance between a read element and a write element by a skew angle, a change in write width in a radial direction, and a deviation of an offset in a writing time. Therefore, to record high-quality servo information, it is necessary to accurately control the pitch between burst signal recording positions.
Conventionally, a technique of representing a track pitch by a multiple regression model, obtaining a correction amount of an offset, and correcting a pattern pitch is known. Also, a technique of checking a ratio between the write element width and the read element width, and determining a read and write offset from the ratio and a signal ratio with a burst signal is known.